1. Field of the Invention
The present invention relates to a catalyst warm-up technique for a diesel engine.
2. Description of the Related Art
Catalysts are widely employed in diesel engines in order to purify exhaust gases. Such catalysts typically do not exhibit purifying activity until warmed to above a predetermined temperature. Accordingly, a warm-up operation to raise the temperature of the catalyst bed is typically performed when starting up a diesel engine.
Diesel engine catalyst warm-up procedures proposed to date include that disclosed in JP11-229973A. This technique involves providing a second, separate EGR passage for warming the catalyst, in addition to the usual first EGR passage. The first EGR passage recirculates exhaust gases to the air intake from a point upstream from the catalyst, while the second EGR passage recirculates exhaust gases to the air intake from a point downstream from the catalyst. Where the catalyst is at low temperature, recirculation of exhaust gases to the air intake from a point downstream from the catalyst via the second EGR passage causes all the exhaust gases to pass through the catalyst, so that catalyst temperature rises more quickly.
Normal operation immediately after the catalyst warm-up operation, however, may cool the catalyst with a substantial amount of exhaust gas flow, thereby deactivating the catalyst. According, there has existed a need for a technique to accelerate catalyst warm up and maintain its activity.
The present invention is directed to solving this problem, and has as an object to provide a technique for accelerating catalyst warm up and maintaining its activity.
The present invention pertains to a diesel engine comprising a combustion chamber, a fuel injection device for injecting fuel into the combustion chamber, a catalyst for purifying exhaust gases from the combustion chamber, and a controller for controlling a plurality of devices of the diesel engine including the fuel injection device. The controller is configured to perform operation in a first warm-up mode in an early warm-up period after startup of the diesel engine, and to perform operation in a second warm-up mode in a late warm-up period after the early warm-up period, so as to accelerate and maintain activation of the catalyst. The first warm-up mode is configured to provide more energy to the catalyst with exhaust gases than a normal operation mode of the diesel engine, which is performed after the late warm-up period. The second warm-up mode is configured to provide exhaust gases of higher temperature to the catalyst than the normal operation mode.
In an embodiment of the present invention, the controller is configured to perform the following three operations in the first warm-up mode: (i) controlling the fuel injection device such that fuel injection is subdivided into pilot injection and main injection; (ii) setting an injection charge proportion for the pilot injection to a level higher than an injection charge proportion for the pilot injection in the normal operation mode, and (iii) retarding an injection timing for the main injection relative to an injection timing for the main injection in the normal operation mode.
The present invention is also directed to an operation method of a diesel engine including a combustion chamber, a fuel injection device for injecting fuel into the combustion chamber, and a catalyst for purifying exhaust gases from the combustion chamber. The method comprises the steps of: performing engine operation in a first warm-up mode in an early warm-up period after startup of the diesel engine, so as to accelerate activation of the catalyst; and performing engine operation in a second warm-up mode in a late warm-up period after the early warm-up period, so as to maintain activity of the catalyst. The first warm-up mode is configured to provide more energy to the catalyst with exhaust gases than a normal operation mode of the diesel engine, wherein the normal operation mode is performed after the late warm-up period. The second warm-up mode is configured to provide exhaust gases of higher temperature to the catalyst than the normal operation mode.
Another aspect of the present invention pertains to a diesel engine comprising: a combustion chamber; a fuel injection device for injecting fuel into the combustion chamber; a catalyst for purifying exhaust gases from the combustion chamber; and a controller for controlling the fuel injection device, wherein the controller performs the following operations: (i) controlling the fuel injection device such that during a warm-up period of the catalyst, fuel injection is subdivided into pilot injection and main injection; (ii) setting an injection charge proportion for the pilot injection during the warm-up period to a level higher than an injection charge proportion for the pilot injection during a normal operation of the diesel engine, and (iii) retarding an injection timing for the main injection during the warm-up period relative to an injection timing for the main injection during the normal operation of the diesel engine.
The present invention may be embodied in various forms such as a diesel engine (a compression ignition internal combustion engine), a catalyst warm-up control device for a diesel engine, a operation method for the engine, a vehicle or moving body employing a diesel engine, and so on.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.